Huge numbers of dinosaurs lie in wait

They are natural history's superstars, yet we know surprisingly little about the diversity of dinosaurs. Now a mathematical model provides an estimate of how many different genera of dinosaurs there were.

The good news is that at least 70% are still be waiting to be found, the analysis suggests. The work could also stoke the debate about what killed the dinosaurs off in the first place.

Steve Wang, a statistician at Swarthmore College, Pennsylvania, and Peter Dodson, a palaeontologist at the University of Pennsylvania, Philadelphia, US, totted up the skeletons found so far from each known dinosaur genus and plugged the figures into an established mathematical model that links observed data to unseen genera.

Only 527 genera have so far been described, but the model estimated that there should be about 1850 in total - leaving plenty yet to be discovered.

Explosion of discoveries

"We are currently living in a dinosaur renaissance, with unprecedented numbers of discoveries every year," Wang says. About as many dinosaurs have been discovered in the past two decades as in all of previous human history, he says, largely because of an explosion of findings in countries such as China and Argentina. The number of genera known from these countries has doubled in the past 20 years.

The trend does not appear to be slowing. "Perhaps Africa will be the next region to blossom," Wang says.

However, not all the remaining genera will be found. The researchers estimate that 46% are "undiscoverable", because they've left no fossils that can ever be found. Ninety per cent of those that are discoverable will be known within 100-140 years, they say.

And what of the dinosaurs' demise? Some palaeontologists argue that they were already dying out before a meteorite strike at the end of the Cretaceous period finished them off, about 65 million years ago.

Final years

When Wang and Dodson compared the dinosaur diversity in the last six million years of the Cretaceous - the Maastrichtian Stage - with the previous six million years they found no change. However, the model the researchers used was not detailed enough to show whether a slight decline had already set in by the time the meteorites struck, Dodson says.

Paul Barrett, a palaeontologist at the Natural History Museum in London, UK, says that climate change and volcanic activity probably contributed to a decrease in dinosaur diversity before the end of Cretaceous, and the meteorite strike finished them off.

Journal reference: Proceedings of the National Academy of Sciences (vol 103, p 13601)

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